Hiroaki Naritomi

Administration of CD34 + cells after stroke enhances neurogenesis via angiogenesis in a mouse model

Thrombo-occlusive cerebrovascular disease resulting in stroke and permanent neuronal loss is an important cause of morbidity and mortality. Because of the unique properties of cerebral vasculature and the limited reparative capability of neuronal tissue, it has been difficult to devise effective neuroprotective therapies in cerebral ischemia. Our results demonstrate that systemic administration of human cord blood-derived CD34(+) cells to immunocompromised mice subjected to stroke 48 hours earlier induces neovascularization in the ischemic zone and provides a favorable environment for neuronal regeneration. Endogenous neurogenesis, suppressed by an antiangiogenic agent, is accelerated as a result of enhanced migration of neuronal progenitor cells to the damaged area, followed by their maturation and functional recovery. Our data suggest an essential role for CD34(+) cells in promoting directly or indirectly an environment conducive to neovascularization of ischemic brain so that neuronal regeneration can proceed.

Prevention of Rat Cerebral Aneurysm Formation by Inhibition of Nitric Oxide Synthase

BACKGROUND Cerebral saccular aneurysm is a major cause of subarachnoid hemorrhage, one of the cerebrovascular diseases with the highest mortality. The mechanisms underlying the development of aneurysms, however, still remain unclear. We have made a series of reports on an animal model of experimentally induced cerebral aneurysms that resemble human cerebral aneurysms in their location and morphology, suggesting that the arterial wall degeneration associated with aneurysm formation develops near the apex of arterial bifurcation as a result of an increase in wall shear stress. Using the animal model and human specimens, we examined the role of nitric oxide (NO) in the degenerative changes and cerebral aneurysm formation. METHODS AND RESULTS Inducible NO synthase (iNOS) was immunohistochemically located at the orifice of human and rat aneurysms. Nitrotyrosine distribution was also seen in the human aneurysm. Although no iNOS immunostaining was found in normal arteries, iNOS immunoreactivity was observed in parallel with the development of early aneurysmal changes in rats. In contrast, during the early development of aneurysm, endothelial NOS immunostaining in the endothelium was weakened compared with that in the control arteries. An NOS inhibitor, aminoguanidine, attenuated both early aneurysmal changes and the incidence of induced aneurysms. A defibrinogenic agent, batroxobin, which may diminish shear stress by reduction of blood viscosity, prevented iNOS induction as well as early aneurysmal changes. CONCLUSIONS The evidence suggests that NO, particularly that derived from iNOS, is a key requirement for the development of cerebral aneurysm. The iNOS induction may be caused by an increase in shear stress near the apex.

Circulating CD34-Positive Cells Provide an Index of Cerebrovascular Function

Background—Increasing evidence points to a role for circulating endothelial progenitor cells, including populations of CD34- and CD133-positive cells present in peripheral blood, in maintenance of the vasculature and neovascularization. Immature populations, including CD34-positive cells, have been shown to contribute to vascular homeostasis, not only as a pool of endothelial progenitor cells but also as a source of growth/angiogenesis factors at ischemic loci. We hypothesized that diminished numbers of circulating immature cells might impair such physiological and reparative processes, potentially contributing to cerebrovascular dysfunction. Methods and Results—The level of circulating immature cells, CD34-, CD133-, CD117-, and CD135-positive cells, in patients with a history of atherothrombotic cerebral ischemic events was analyzed to assess possible correlations with the degree of carotid atherosclerosis and number of cerebral infarctions. There was a strong inverse correlation between numbers of circulating CD34- and CD133-positive cells and cerebral infarction. In contrast, there was no correlation between the degree of atherosclerosis and populations of circulating immature cells. Analysis of patients with cerebral artery occlusion revealed a significant positive correlation between circulating CD34- and CD133-positive cells and regional blood flow in areas of chronic hypoperfusion. Conclusions—These results suggest a possible contribution of circulating CD34- and CD133-positive cells in maintenance of the cerebral circulation in settings of ischemic stress. Our data demonstrate the utility of a simple and precise method to quantify circulating CD34-positive cells, the latter providing a marker of cerebrovascular function.

Correction of INR by prothrombin complex concentrate and vitamin K in patients with warfarin related hemorrhagic complication

We investigated the effect of prothrombin complex concentrate (PCC, median 500 IU) and vitamin K (10-20 mg) or either on blood coagulation and clinical findings in 17 patients with major hemorrhagic complication during warfarin treatment. Their international normalized ratio (INR) at admission was median 2.7 (2.0-above 10.0). In 11 patients treated with PCC and vitamin K, INR decreased to median 1.13 (0.91-1.36) 10 min after the administration with elevation of plasma levels of coagulant factors II, VII, IX, X and protein C.INR decreased abruptly after the administration of PCC without vitamin K in two patients but it increased again 12-24 h after, with decrease of coagulant factors levels. In one of them, a hematoma of the brain enlarged with INR re-increase 12-24 h after the administration. In four patients treated with vitamin K alone, INR decreased slowly from 2.69 (1.03-3.35) to 1.28 (1.25-1.44) 12-24 h after the administration in parallel with gradual increase of the coagulant factors.PCC administration with or without vitamin K seems to be more effective in rapidly correcting increased INR levels than vitamin K treatment without PCC. PCC without vitamin K may result in re-increase of INR and clinical deterioration.

Takotsubo Cardiomyopathy in Acute Ischemic Stroke

Takotsubo cardiomyopathy, which is characterized by transient left ventricular apical ballooning, is a known complication of subarachnoid hemorrhage. The aim of this study was to identify the clinical characteristics of acute ischemic stroke patients who experienced development of takotsubo cardiomyopathy.

The VITATOPS (Vitamins to Prevent Stroke) Trial: Rationale and Design of an International, Large, Simple, Randomised Trial of Homocysteine-Lowering Multivitamin Therapy in Patients with Recent Transient Ischaemic Attack or Stroke

Background: Epidemiological studies suggest that raised plasma concentrations of total homocysteine (tHcy) may be a common, causal and treatable risk factor for atherothromboembolic ischaemic stroke. Although tHcy can be lowered effectively with small doses of folic acid, vitamin B12 and vitamin B6, it is not known whether lowering tHcy, by means of multivitamin therapy, can prevent stroke and other major atherothromboembolic vascular events. Purpose: To determine whether vitamin supplements (folic acid 2 mg, B6 25 mg, B12 500 µg) reduce the risk of stroke, and other serious vascular events, in patients with recent stroke or transient ischaemic attacks of the brain or eye (TIA). Methods: An international, multi-centre, randomised, double-blind, placebo-controlled clinical trial. Results: As of November 2001, more than 1,400 patients have been randomised from 10 countries in four continents. Conclusion: VITATOPS aims to recruit and follow up 8,000 patients between 2000 and 2004, and provide a reliable estimate of the safety and effectiveness of dietary supplementation with folic acid, vitamin B12, and vitamin B6 in reducing recurrent serious vascular events among a wide range of patients with TIA and stroke.

Baseline NIH Stroke Scale Score predicting outcome in anterior and posterior circulation strokes

Objective: The NIH Stroke Scale (NIHSS) may not appropriately assess the spectrum of posterior circulation (PC)–related neurologic deficits. We determined the cutoff baseline NIHSS score that predicts independent daily life activity during the chronic stage in anterior circulation (AC) vs PC ischemic strokes. Methods: A total of 310 consecutive patients hospitalized within 3 days after the onset of an ischemic stroke were prospectively enrolled in the study. Patients on thrombolytic therapy were excluded. In all patients, infarcts and vascular lesions were identified primarily using magnetic resonance techniques. A favorable outcome was defined as a modified Rankin Scale score of ≤2 at 3 months poststroke. Results: In 101 patients with PC stroke, the total baseline NIHSS score was lower (p < 0.001), and the subscores of ataxia (p < 0.001) and visual fields (p = 0.043) were higher than in 209 patients with AC stroke. Multivariate-adjusted OR for the favorable outcome in patients with PC vs AC stroke was 2.339 (95% CI 1.331–4.109, p = 0.003). A low baseline NIHSS score was independently predictive of a favorable outcome in both patients with PC (OR 1.547, 95% CI 1.232–1.941) and AC (1.279, 1.188–1.376) stroke. The optimal cutoff scores of the baseline NIHSS for the favorable outcome were ≤5 for patients with PC stroke (sensitivity, 84%; specificity, 81%) and ≤8 for patients with AC stroke (sensitivity, 80%; specificity, 82%). Conclusions: The cutoff score of the baseline NIH Stroke Scale (NIHSS) for a favorable chronic outcome was relatively low in patients with PC stroke compared to patients with AC stroke. The NIHSS appears to have limitations with respect to its use when comparing the neurologic severity of PC and AC stroke.

Role of Insulin Resistance Associated With Compensatory Hyperinsulinemia in Ischemic Stroke

BACKGROUND AND PURPOSE Although insulin resistance and hyperinsulinemia play a crucial role in the pathogenesis of atherosclerosis, little is known about their roles in ischemic stroke. The purpose of this study was to clarify whether insulin resistance and hyperinsulinemia are causative factors in the pathogenesis of ischemic stroke. METHODS Thirty-four consecutive patients with ischemic stroke, who were normotensive, nondiabetic, and not obese, were classified into three groups--atherothrombotic infarction (n = 16), lacunar infarction (n = 10), and cardioembolic infarction (n = 8)--based on clinical findings, brain imaging, and cerebral angiography. Both oral glucose tolerance tests and lipid analyses were performed. Insulin sensitivity was determined by the steady state plasma glucose method with the use of octreotide acetate. Data were compared with those of healthy control subjects (n = 15). RESULTS Steady state plasma glucose levels were significantly higher in the atherothrombotic infarction group compared with control subjects and the other two stroke groups, indicating the presence of insulin resistance in patients with atherothrombotic infarction. In the atherothrombotic infarction group, the 2-hour insulin area (area under the plasma insulin concentration curve) during a 75-g oral glucose tolerance test was significantly increased and dyslipidemic changes (increased triglyceride and apolipoprotein B, decreased high-density lipoprotein) were observed, whereas these changes were not found in the lacunar infarction and cardioembolic stroke groups. CONCLUSIONS Insulin resistance in association with compensatory hyperinsulinemia and dyslipidemia may be an important pathogenetic factor underlying the development of atherothrombotic infarction.

Improved method for noninvasive measurement of regional cerebral blood flow by 133Xenon inhalation. Part I: description of method and normal values obtained in healthy volunteers.

A clinical method for noninvasive measurement of regional cerebral blood flow (rCBF) and blood volume (rCBV) is described, basedon Obrists 10 minute, desaturation method after 1 minute inhalationof 133Xe. Sixteen collimated probes are placed over both hemispheres and brain stem-cerebellar regions. End-tidal 18>Xe curves are used for correction of recirculation. KEV discriminators are set to record gamma and x-ray activity separately. Values are printed out automatically by a computer on a brain map. Extracerebral contamination is reduced by 1) computing curves from gamma activity, 2) applying pressure on the scalp beneath the probes, 3) 1 minute inhalation of 133Xe and recording desaturation curves for 10 minutes, thereby minimizing slow clearance from extracranial tissues. Normal values for both fast and slow compartments are reproducible and are in good agreement with the carotid injection method. The speech dominant hemisphere has higher flow than the right under conditions described. Posterior portions of the cranium over the cerebellum andbrain stem appear to have higher flow gray values than the cerebral cortex. Gray matter flow decreases with advancing age.

Flow Thresholds for Cerebral Energy Disturbance and Na+ Pump Failure as Studied by In Vivo 31P and 23Na Nuclear Magnetic Resonance Spectroscopy

The relationships among CBF, cerebral energy metabolism, Na+ pump activity, and electrocorticograms (ECoG) following graded hypotension were studied in 48 gerbils. Energy metabolism and Na+ pump activity were estimated by in vivo 31p and 23Na nuclear magnetic resonance (NMR) spectroscopy, and CBF was determined by [14C]iodoantipyrine methods at the end of the experiments. The CBF measured in normotensive animals was 0.51 ± 0.07 ml/g brain/min. Following graded hypotension, no 31P spectral change was observed until CBF fell to 0.21–0.27 ml/g brain/min, at which level the intracellular pH began to decrease in association with ECoG voltage reduction. At a CBF level of 0.18–0.23 ml/g brain/min, phosphocreatine (PCr) began to decrease in association with inorganic phosphate (Pi) elevation. At this level, ECoG became isoelectric, although no adenosine triphosphate (ATP) change yet resulted. At a flow level of 0.12–0.14 ml/g brain/min, ATP began to decrease gradually. At 0.04–0.05 ml/g brain/min, PCr and ATP virtually disappeared, and the 23Na signal intensity suddenly changed. The present study demonstrated flow thresholds for the development of tissue acidosis, PCr–Pi changes, and ATP reduction. It appears that functional suppression occurs prior to ATP changes, whereas Na+ pump failure results after ATP depletion.